1. Field of the Invention
The present invention relates to a silver halide photographic emulsion and a photographic light-sensitive material using the same and, more particularly, to a silver halide grain having a novel form and a method of manufacturing the same.
2. Description of the Related Art
In recent years, as small formatting of a film has progressed or photographing conditions have been diversified, a strong demand has arisen for a film having high sensitivity and capable of exposure within a wide range of applications. Under the circumstances, a silver halide in an emulsion must have, as its basic performance, high sensitivity, a low fogging property and a small grain size. Improvements in such performance contribute to progress in silver halide light-sensitive materials as a whole. In order to manufacture an emulsion having high sensitivity and small grain size, it is preferred to prevent efficiency-lowering and increase quantum efficiency of a grain itself in an exposure process. Possible factors of the low quantum efficiency are recombination, latent image dispersity, a competing electron trap derived from a lattice defect, and the like. A number of conventional techniques have been proposed for a composite silver halide crystal formed by epitaxially junctioning a crystal having a halogen composition different from that of a substrate grain to a specific portion of the grain upon silver halide grain formation. For example, JP-A-53-103725 (37 JP-A-" means unexamined published Japanese patent application) discloses a method of epitaxially growing silver chloride crystals on a silver iodide crystal substrate capable of absorbing light of a long wavelength to form grains having spectral sensitivity of silver iodide and a developing property of silver chloride, thereby improving photographic sensitivity. JP-A-59-133540 discloses a method of manufacturing a grain having high sensitivity by epitaxially growing a silver salt at a portion, selected in the presence of a site director, of a host grain having an average aspect ratio of less than 8 and surrounded mainly by (111) crystal planes.
In the above junctioned grain, the location of a junction is defined to a surface, an edge, a corner or a combination thereof by the site director. Therefore, as shown in FIG. 3 of JP-A-59-133540, even if the junction is limited to a corner, a single grain has substantially six or more junctions. In addition, as shown in FIG. 5 of JP-A-59-133540, when epitaxial growth on surface is performed, junctions spread on the overall grain surfaces and therefore the number of point of junction cannot be counted.
JP-A-53-103725 discloses a method of epitaxially growing silver chloride on a substrate consisting of .beta.-phase silver iodide crystals having a wurtzite crystal structure. JP-A-53-103725 describes that a silver chloride epitaxially grown portion is generally present one for each grain. In the case of a substrate grain consisting of silver bromide, silver chloride, silver iodobromide, silver bromochloride or silver chloroiodobromide having a rock-salt structure, however, no junctioned grain having only one junction has been reported in any published literatures including JP-A-53-103725.
JP-A-59-133540 describes that a silver salt epitaxially grown portion can function as an electron trap in a latent image formation process. If the latent dispersity is considered as a factor of the low quantum efficiency, the conventional junctioned grain having a plurality of junctions or a wide junction area per grain easily causes latent dispersity and provides only insufficient high-intensity sensitivity.